The proposals outlined relate to three different aspects of transport across biological membranes. a. How are proteins that are destined for locations other than the cytoplasmic site of their synthesis, 'exported' across the membrane boundary? Methods are being developed to mutate the signal sequence of E. coli beta-lactamase by in vitro chemical mutagenesis of a segment of the gene that includes the signal sequence of this enzyme. b. What is the precise labeling pattern produced when a transmembrane protein, the coat protein from the bacteriophage M13, is photo-labeled by the carbene derived from (3H)adamanthyl diazirine? c. What is the scope of the 'illicit transport' approach to the smuggling of relatively small foreign molecules into a bacterial cell? The extent to which the oligopeptide transport system can be used for illicit transport will be delineated, with a view both to experiments concerning the delivery of antibiotics, and to experiments probing the distribution of membrane proteins as seen from the cytoplasmic face of the membrane.